Floating hatchery and net cage culture of Penaeus indicus in the Straits of Johore, Singapore

Abstract

A simple floating hatchery system with partially submerged tanks (bags made of flexible, plastic-coated fabric) was used to rear the larvae of Penaeus indicus. A total of 1.96 million active nauplii were reared in 6000-l tanks at average densities of 67 nauplii and 42 nauplii/l of tank capacity. Development time from spawning to metamorphosis was 9 days and the average survival rate of nauplii to age PL6 was 49%. From age PL6, post-larvae were reared in nursery net cages (6 × 3 × 0.6 m) in the sea. At densities of 50 000-60 000 post-larvae/cage, the average survival rate from age PL6 to age PL20-22 was 78%; from age PL20-22 to age PL37-44 at densities of 25 000/cage it was 83%. One batch of juveniles was stocked in a prawn pond at age PL27 and another was stocked at high densities in two sizes of net cages at age PL37-50. The prawns grown in the pond reached a mean size of 9 g after 76 days (at age PL103). In large net cages (5 × 5 × 2.5 m) stocked at a density of 80/m2, prawns reached a marketable size of 9.8 g after 113 days (at age PL157) with an average survival rate of 32%. Based on these results, the costs of producing post-larvae and juveniles using the floating hatchery and nursery net cage system and of producing live prawns of marketable size by net cage culture were calculated. Modifications in the net cage culture techniques employed are recommended to improve growth and survival rates and reduce production costs. © 1987.